Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a recording material by an electrophotographic process.
Description of the Related Art
Conventionally, for image forming apparatuses for forming images on a recording material using toner (developer) such as electrophotographic apparatuses or electrostatic recording apparatuses, a cleanerless system (toner recycle system) has been proposed from a viewpoint of simplification of an apparatus configuration and elimination of waste. The system eliminates an exclusive drum cleaner, which is surface cleaning means after a transfer step of a photosensitive drum, moves transfer residual toner on the photosensitive drum after transfer to a development roller during a developing step to remove it from the photosensitive drum, and recovers the residual toner in a development device and reuses the same. The simultaneous developing/cleaning for removing residual toner on a photosensitive drum during a developing step is a method of recovering the residual toner on the photosensitive drum after a transfer step by toner recovery bias for recovering in a developing step at an image formation step or later. The toner recovery bias is a fog removing potential difference Vback, which is a potential difference between a DC voltage applied to a development roller (developer bearing member) and surface potential of the photosensitive drum (image bearing member). According to the method, since the transfer residual toner is recovered in the development device and reused in the next step or later, work such as disposing the waste toner and such becomes unnecessary and troublesome maintenance can be reduced. Since it is cleanerless, it is advantageous in terms of space and the image forming apparatus can be significantly downsized.
In an image forming apparatus using the simultaneous developing/cleaning system, it is important to reduce the transfer residual toner on the photosensitive drum after a transfer step, completely recover the toner to the development device in a developing step, and prevent the toner from appearing in the next image formation. Because, there is a possibility in which not all transfer residual toner on the photosensitive drum after a transfer step cannot be recovered in a developing step and a recovery residue ghost image or a toner scattering image appears.
For instance, in Japanese Patent No. 4510493, a mono component magnetic contact development system is proposed as a development device adopting the simultaneous developing/cleaning. The system is to perform development by carrying magnetic developer (magnetic toner) on a development sleeve (developer bearing member) containing magnetic field generating means and bringing it into contact with a surface of the photosensitive drum.
In Japanese Patent Application Publication No. 2003-173053, it is proposed, in a development device adopting the simultaneous developing/cleaning, to reduce an absolute value of a developing bias in image formation on a rear face to be smaller than in image formation on a front face so as to reduce an influence of a change in the moisture content of a recording material on the image quality.
When both side image formation is performed, transferability changes between a front face (a recording material that does not pass a fixing device) of the recording material and a rear face (a recording material that once passed the fixing device). With the above-described conventional configuration, there is a case where white background fogging becomes worse and a change in recovery residue ghost occurs caused by a change in transferability in both side image formation, and the image quality becomes unstable. In recent years, with requirement for saving paper use being on the rise to conserve resources, duplex printing has become more prevalent. This presents an important challenge to address since high image quality is required also in both side image formations.